Generally, diamonds obtained by synthesis at high pressure and high temperature are those known as type lb and contain hundreds of ppm of nitrogen in their crystalline lattice. Due to the structural nitrogen content, the color of the diamond crystals ranges from light yellow to dense yellow, a limitation that usually is reflected in their having a lower value for the jewelry industry.
On the other hand, this color can be extracted by introducing a nitrogen scavenger in the reaction area mixed with the solvent. In this manner, the solvent is free of the dissolved nitrogen, since the nitrogen reacts with the scavenger, forming compounds such as nitrides, carbides, various intermediate compounds and their combinations thereof. The effect of this competition for nitrogen between the scavenger and the carbon is that less nitrogen enters the diamond crystalline network that is growing, providing crystals that are substantially free of nitrogen.
These crystals are of the type known as type IIa, due to the rarity of said crystals in nature, since they are colorless, their excellent properties of thermal conductivity and hardness making them highly valued in the market.
The inconvenience of these crystals is that their production is extraordinarily difficult, especially because the competition reaction caused by the nitrogen scavenger produces many compounds that remain in suspension, making possible their entry into the monocrystals, during the growth process, as metallic inclusions. This fact makes obtaining large size and pure type IIa crystals difficult. Also, achieving the elimination of nitrogen from the crystalline lattice of the diamond implies that during the process, other type of impurities may enter, such as is the case with boron. Diamond crystals with boron impurities are known as type IIb diamonds and are blue colored.